I'm sure you've heard that folk have changed their polling times downward so that email seems to arrive in real time. So as more folk do that the email server load increases. All the email apps I know of can retry and since it eventually gets delivered, no one says it's broke.
About switching. If the email app would silently check and only report failures after a dozen attempts in say a hour then that could fix it for most folk.
I have Windows XP and I use Outlook Express for my email. I use Earthlink as my ISP and I am using a DSL modum. Between 4 AM and 6 AM my Outlook Express works very fast and very well. After 6 AM Outlook Express begins to take much longer to connect and then download my emails. Then about 9 AM my Outlook Express begins to fail to connect to one or more of my five accounts, but it always connects to at least two of them. It's always different accounts that fail with different tries. This slowness and these failures continue until about 8 PM. My modum tests fine throughout the day at about 3 mbps, Earthlink checked and checked and said there must be something wrong with my Outlook Express software; that I should reload it. Another person said switching to Outlook would fix my problem. How can my Outlook express be fine at 4 AM but horrible at 2 PM? Thanks.